- Aalto, Alvar (Hugo Alvar Henrik) (1898–1976)

- Abbe, Ernst (1840–1905)

- Abel, Neils Henrik (1802–1829)

- Abercrombie, (Leslie) Patrick (1879–1957)

- Abetti, Giorgio (1882–1982)

- Ackerman, James S(loss) (1919– )

- Ackerman, Nathan W(ard) (1909–1971)

- Adam (architects)

- Adams, John Couch (1819–1892)

- Adams, Robert McC. (McCormick) (1926– )

- Adams, Walter Sydney (1876–1956)

- Addison, Thomas (1793–1860)

- Adler, Alfred (1870–1937)

- Adler, Alfred (1870–1937)

- Adler, Dankmar (1844–1900)

- Adrian, Edgar Douglas (1889–1977)

- Agassiz, (Jean) Louis Rodolphe (1807–1873)

- Agnesi, Maria Gaetana (1718–1799)

- Agricola, Georgius (1490–1555)

- Aiken, Howard Hathaway (1900–1973)

- Airy, George Biddell (1801–1892)

- Aitken, Robert Grant (1864–1951)

- Alberti, Leon Battista (1404–1472)

- Alder, Kurt (1902–1958)

- Aleksandrov, Pavel Sergeevich (1896–1982)

- Alessi, Galeazzo (1512–1572)

- Alexander, Hattie Elizabeth (1901–1968)

- Alfvén, Hannes Olof Gösta (1908–1995)

- Alhazen, Abu Alī al-Hassan ibn al-Haytham (c. 965–1038)

- Allport, Gordon (Willard) (1897–1967)

- Alpher, Ralph Asher (1921– )

- al-Sufi (903–986)

- Alter, David (1807–1881)

- Alvarez, Luis Walter (1911–1988)

- Alzheimer, Alois (1864–1915)

- Ambartsumian, Viktor Amazasp Amazaspovich (1908–1996)

- Ammanati, Bartolommeo (1511–1592)

- Ampère, André-Marie (1775–1836)

- Amsler-Laffon, Jakob (1823–1912)

- Anastasi, Anne (1908–2001)

- Anaximander the Elder (c. 611–547 BC)

- Anderson, Carl David (1905–1991)

- Anderson, Philip Warren (1923– )

- Ando, Tadao (1941– )

- Andrews, Thomas (1813–1885)

- Andronicus II Palaeologus (1260–1332)

- Angell, James (Rowland) (1869–1949)

- Ångström, Anders Jonas (1814–1874)

- Annear, Harold Desbrowe (1865–1933)

- Anning, Mary (1799–1847)

- Anokhin, Piotre Kuzmich (1897–1974)

- Anthemius (lived 5th–6th century AD)

- Antoniadi, Eugène Marie (1870–1944)

- Apgar, Virginia (1909–1974)

- Apollodorus (lived AD 97–130)

- Apollonius of Perga (c. 245–c.190 BC)

- Appert, Nicolas François (c.1750–1841)

- Appleton, Edward Victor (1892–1965)

- Arago, (Dominique) François (Jean) (1786–1853)

- Archer, John Lee (1791–1852)

- Archer, Thomas (1668–1743)

- Archimedes (c. 287–212 BC)

- Ardemáns, Teodoro (1664–1726)

- Argand, Jean Robert (1768–1822)

- Argelander, Friedrich Wilhelm August (1799–1875)

- Argyris, Chris(topher) (1923– )

- Argyropoulos, John (Janos) (c. 1415–1487)

- Aristarchos (c. 320–c. 250 BC)

- Aristotle (384–322 BC)

- Arkwright, Richard (1732–1792)

- Armelagos, George J(ohn) (1936– )

- Armstrong, Edwin Howard (1890–1954)

- Armstrong, William George (1810–1900)

- Arnolfo di Cambio (c. 1245–c. 1302)

- Arp, Halton Christian (1927– )

- Arrhenius, Svante August (1859–1927)

- Artin, Emil (1898–1962)

- Arup, Ove (1895–1988)

- Asplund, (Erik) Gunnar (1885–1940)

- Aston, Francis William (1877–1945)

- Atkinson, Robert D'escourt (1898–1982)

- Attenborough, David Frederick (1926– )

- Audubon, John James Laforest (1785–1851)

- Auer, Carl

- Avery, Oswald Theodore (1877–1955)

- Avicenna (980–1037)

- Avogadro, Amedeo (1776–1856)

- Ayrton, Hertha (Phoebe Sarah) Marks (1854–1923)

- Ayrton, William Edward (1847–1908)